This invention relates to a soft-magnetic film having high saturation magnetic-flux density as well as to a magnetic head utilizing this film (including a thin-film magnetic head).
Recording mediums for high-density magnetic recording/reproduction (or writing/reading) are required to have high coercive force (Hc), whereas materials for magnetic-recording heads are required to have high saturation magnetic-flux density (Bs). Conventionally, there have been available only limited kinds of soft-magnetic head materials exhibiting high Bs values: Fe-system and Co-system amorphous alloys as well as Sendust alloys may be mentioned as examples of such materials. Alloys of the above-mentioned types which exhibit around 10,000 Gauss for practical use are known. These alloys can provide low coercive force (Hc) and high magnetic permeability (.mu.i) as well as high saturation magnetic-flux density.
In order to realize more efficient magnetic recording/reproduction, materials exhibiting still higher Bs values must be used. In this regard, amorphous alloy films of Fe-system are inadequate since they do not easily allow a sufficiently low magnetostriction to be obtained Besides, they have great difficulty providing satisfactory stability in soft-magnetic properties when heat-treated. Amorphous materials of Co-system alloys allow a sufficiently low magnetostriction to be realized. In addition, some of them can provide satisfactory stability for heat treatment. However, the maximum Bs value they can provide is at most around 14,000 Gauss. From the practical point of view, those having high Bs values are still inadequate in stability for heat treatment As for Sendust-alloy thin films, they are relatively free from the problem of inadequate thermal stability. However, the soft-magnetic properties they can provide are by no means sufficient, the maximum practical Bs value they exhibit is at most in the range 11,000 to 12,000 Gauss.
For practical use, head materials are required which exhibit a Bs value of 15,000 Gauss or more and which have satisfactory soft-magnetic properties (low coercive force (Hc), high initial permeability (.mu.i) and low magnetostriction (.lambda.s)).
Various reports have been made on the magnetic properties of Fe-Co-Ni ternary alloy system which are known as "Perminvar Alloys". However, these alloys are restricted to bulk (solid) materials. As to their soft-magnetic properties, substantially nothing is known about the properties of thin-film materials which generally exhibit considerable surface orientation even when the composition is the same.
Thin alloy-films containing as their main components Fe, Co and Ni are referred to here. The films are manufactured by evaporation or electrodeposition and have a face-centered cubic-lattice structure. As shown in FIG. 1, the saturation magnetic-flux density of such thin films depends principally on the amount of Ni atoms; when Ni&lt;70 at%, a soft-magnetic thin film exhibiting a Bs value of above 12,000 can be obtained. This Bs value is not to be attained with conventional soft-magnetic thin films. However, if Ni.ltoreq.20 at%, the face-centered cubic-lattice structure has no stability at room temperature, whereas the body-centered cubic-lattice structure becomes stable, which quite adversely affects the soft-magnetic properties of the thin film. As shown in FIG. 2, this also applies to the case where Fe.gtoreq.75 at% (i.e., 20&lt;Ni&lt;70 [%] and Fe&lt;75% are the requisite conditions).
Normally, the crystal magnetic anisotropy constant and magnetostriction constant greatly influence the soft-magnetic properties. They not only depend on the alloy element composition, but differ greatly both in absolute value and sign in accordance with the incrystallographic-plane value. Furthermore, they depend in general greatly on the surface orientation of the thin-film material as well as the grain size and grain configuration thereof Accordingly, the data on these thin films differ from that on the above-mentioned conventional alloys in the form of bulk materials even when the composition is the same.